Giki Zero Footprint Methodology

Overview

Giki Zero is a step by step guide to help people understand, track and lighten their footprint on the planet. It combines a detailed, science based, carbon footprint tool and over 120 steps to help people find ways to reduce their footprint which suit their lifestyle and budget.

We provide our methodology so that users can understand the calculations behind Giki Zero. We also hope it will be useful to other people who are looking to calculate individual carbon footprints. If you do use our methodology please do let us know and cite Giki Zero where appropriate.

Giki Zero provides estimates for a person’s environmental impact based on a series of footprint models which are categorised in sections. These are home, transport, food, purchases, services and trees.

Footprint estimates are based on consumption which in turn can be average (typically the UK average), estimate or actual based on the amount of information that a user provides.

Consumption estimates are then multiplied by conversion factors in order to estimate footprints for carbon, land and water. These are carbon dioxide equivalents (CO2e), water usage (litres, l) or land usage (square meters, m2).

Models are for the individual or shared across the household. For example a diet footprint estimates the impact from an individual’s diet but an electricity footprint calculates the impact for a whole house and so is shared across household members.

User input is given based on the current calendar year and continuation is assumed from period to period.

All of the estimates provided in Giki Zero are exactly that, estimates. Footprint models will evolve over time based on improved estimation as well as updated, or improved, data. For example a number of the main data sets used by Giki Zero update annually and see material changes in impact measurement both due to calculation enhancements and changes in impact as providers of goods and services respond to the need for decarbonisation. Where individuals want a more personalised footprint with lower estimation error they should enter actual data whenever possible. This is possible in the majority of Giki Zero footprint models.

Giki’s mission is to help people live more sustainably and so a full methodology is provided to ensure both transparency of how footprints are calculated but also as a source for others trying to do the same or for others to provide suggestions for how Giki Zero can improve. Where possible data sources have been chosen which are publicly available.

Home

Electricity Footprint

Electricity footprints are calculated for the household as a function of electricity used and the CO2e emissions per unit of that electricity.

Average values are based on mean electricity consumption for all dwelling types based on double adult occupancy and average UK supplier CO2e emissions.

Estimates are taken from the National Energy Efficiency Data using property type and a bedroom proxy based on quartile ranges. CO2e averages are from electricityinfo.org and Defra conversion factors are used to account for transmission and distribution emissions. The latter explains why green electricity providers still have an electricity carbon footprint.

Household usage actuals are user inputs combined with actual CO2e emissions by supplier, or UK average, taken from electricityinfo.org.

Sources

Updates and model specifications

  • UK data
  • Per Household model
  • Refinements taken from various sources including Energy Savings Trust

Gas Footprint

Gas footprints are calculated for the household based on the consumption (average, estimated, or actual) in kilowatt-hours, multiplied by the CO2e/kwh of the gas supplier (either the model average, or a specific supplier if given) from Defra conversion factors. Providers of green gas are adjusted supplier by supplier using their % of green gas out of total gas.

Average values are based on mean gas consumption for all dwelling types based on double adult occupancy and average UK supplier CO2e emissions.

Consumption estimates are taken from the National Energy Efficiency Data using property type and a bedroom proxy based on quartile ranges.

Users can provide their meter readings in either kwh or m3.

Sources

Updates and model specifications

Water Footprint

Carbon footprints from water usage (the amount of CO2e emitted to supply and household with water) are calculated for a person based on the consumption (average, estimated, or actual) in m3 multiplied by carbon emissions from Defra conversion factors accounting for both supply and treatment.

Water footprint calculations are based on the user’s consumption (average, estimated or actual) in m3. Averages are based on medium usage per person for a two or three person household. Estimates are based on a 2 person household.

Sources

Updates and model specifications

  • UK data
  • Per Household model

Oil Footprint

Oil carbon footprints are calculated for a household based on consumption (estimated or actual) in litres multiplied by carbon emissions from Defra conversion factors for heating oil. For estimated usage low, medium, high gas usage is taken from Ofgem and converted to the same energy requirements from oil.

Because under 5% of the UK population have oil fired heating we use a median of zero for the typical UK person.

Sources

Updates and model specifications

  • UK data
  • Per Household model

Wood Footprint

Wood footprints are calculated for the household as a function of wood used and the CO2e emissions per unit of that wood.

Average values are not included as the median wood consumption is zero.

Sources

Updates and model specifications

  • Per Household model
  • Refinements are based on DEFRA outside of scope estimates and with a default that individuals use sustainably sourced wood or gather it themselves.

Waste Footprints

Household waste carbon footprints are calculated for a household based on consumption (average, estimated or actual) in kg multiplied by carbon emissions for different waste types from Defra conversion factors.

Average and estimated waste is taken from WRAP studies with inclusion of large items from the same source. Estimates of recycling rates chosen by users correspond to a scaling factor where the maximum recyclable remains within the boundaries of consumer outcomes.

Sources

Updates and model specifications

  • UK data
  • Per Household model
  • Assumes that households have food waste recycling

House maintenance footprints

House maintenance carbon footprints are calculated for a household but are in early stages given a lack of LCA (Life Cycle Analysis) data looking at house repairs and services. As an initial approximation CO2e per £ spent is calculated using average household spending and carbon footprint data and this multiplied by ONS spending on house maintenance and repair.

Sources

Updates and model specifications

  • UK data
  • Per Household model

Transport

Tube Footprint

Tube carbon footprints are calculated for a person based on consumption (average or estimated) in km travelled multiplied by carbon emissions per km from Defra conversion factors.

Averages distances are from the National Travel Survey and average journeys taken are from the same source.

Sources

Updates and model specifications

  • UK data
  • Per Person model

Rail Footprint

Rail carbon footprints are calculated for a person based on consumption (average or estimated) in km travelled multiplied by carbon emissions per km from Defra conversion factors.

Averages distances are from the National Travel Survey. Distance travelled based on time is taken from a sample of trips using Google maps.

Sources

Updates and model specifications

  • UK data
  • Per Person model

Taxi Footprint

Taxi carbon footprints are calculated for a person based on consumption (average, estimated or actuals) in km travelled multiplied by carbon emissions per km from Defra conversion factors using per km data.

Averages distances are from the National Travel Survey and average journeys and total miles are from the same source.

Sources

Updates and model specifications

  • UK data
  • Per Person model

Bus Footprint

Bus carbon footprints are calculated for a person based on consumption (average, estimated or actuals) in km travelled multiplied by carbon emissions per km from Defra conversion factors using per km data.

Averages distances are from the National Travel Survey and average journeys and total miles are from the same source combining different bus modes.

Sources

Updates and model specifications

  • UK data
  • Per Person model

Cruise and Ferry Footprints

Cruise carbon footprints are calculated for a person based on consumption (average, estimated or actuals) in carbon emissions per day using averages from cruise line meta study. Ferry footprints are calculated based on distance travelled using Defra conversion factors. Average distances travelled are from UK Sea Passenger stats.

Distances are from searoutes.com and with main routes taken from UK government sea passenger statistics.

Sources

Updates and model specifications

  • UK data
  • Per Person model

Car Footprint

Car usage carbon footprints are calculated for a person based on consumption (average, estimated or actuals) in km travelled multiplied by carbon emissions per km from Defra conversion factors using per km data for different car types. Car types are estimated based on size and engine or actuals based on data from the vehicle certification agency. Average distances are taken from the National Travel Survey.

Car ownership carbon footprints are calculated using the World Auto Steel UCSB Model 5 for different engine types and size. Production and lifecycle values are computed and adjusted for average car lifetime and a per annum estimate is then calculated on a straight line basis.

Sources

Updates and model specifications

  • UK data
  • Per Person model

Flight footprint

Flight carbon footprints are calculated for a person based on consumption (average, estimated or actuals) in km travelled multiplied by carbon emissions per km from Defra conversion factors using per km data adjusted for different aircraft classes.

Average distances and average CO2e per km are a weighted average of short, medium and long haul flying for a typical UK person using Department of Transport data. Estimated distances are calculated by using common destinations for short, medium and long haul flights with short, medium and long haul definitions from eurocontrol. Actual distances are calculated on a great circle basis using airport latitude and longitude from openflights.

Sources

Updates and model specifications

  • Global data
  • Personal modal

Motorbike Footprint

Motorbike carbon footprints are calculated for a person based on consumption (average, estimated or actuals) in km travelled multiplied by carbon emissions per km from Defra conversion factors using per km data adjusted for different motorbike types.

The UK median is taken for the typical UK person which is zero as only a small proportion of the population ride a motorbike.

Sources

Updates and model specifications

  • UK data
  • Per Person model

Food

Diet Footprint

Diet carbon, land and water footprints are calculated for a person based on consumption (average, estimated or actuals) in portions of different foods groups multiplied by a conversion factor per kg for food, per m2 for land and per litre for water for those food groups.

Average portion consumption is calculated using the National Diet and Nutrition Survey for 19-64 year old adults consuming a 2,500 calorie diet based on representative food groups. Calorie intake is adjusted for under reporting using data from the Behavioural Insights team and assuming a calorie intake that is sufficient to maintain current weights. In order to adjust calories to portions McCance and Widdowson are used for calories and own estimates, based on desk research, for portion sizes. The result is a per gram per food group assessment of average UK consumption.

For estimated diets portion sizes are adjusted to account for different dietary guidelines. For example the vegetarian diet excludes all meat and fish while the no red meat diet does the same for beef and lamb only. Overall calorie consumption is maintained at the same level normally by scaling up other food groups to account for food groups excluded although in the case of some diets legumes (which are not represented in the NDNS diets) and other food groups are scaled up by a greater amount in order to ensure a balanced overall diet. Diets described as “mainly” plant based or vegetarian follow the same process using a weighted average where 90% of the diet is plant based or vegetarian whilst 10% is based on the typical UK diet.

Calculations for the CO2e, m2 and litres per kg are taken from academic meta studies including Poore and Nemecek (2018), WRAP (2013) and others. These studies are combined, where necessary using a common framework for food categories following Foodex. Averages are taken across food groups and studies in order to mitigate the impact of wide ranges of outcomes for different foods based on LCA boundaries, geographical variation and growing and processing differences.

With portions of food by weight and food group and environmental impacts for food groups overall diets are then calculated as a product of both.

Sources

Updates and model specifications

  • UK diet but with calorie adjustment can represent global
  • Academic studies periodic

Food waste Footprint

Food waste carbon, land and water footprints are calculated for a person based on the proportion of their diet’s carbon, land and water footprint (average, estimated or actuals) that is thrown away. As such a lower impact diet (e.g. mainly plant based vs typical UK diet) will have a proportionality lower food waste impact.

Average food waste per person is taken from WRAP’s overall statistics on edible and inedible food waste for the UK population and adjusted for population at the point of the statistical release. Note that this covers the carbon footprint of food waste to the “house door”. Any food waste impacts from landfill or composting are assessed in home waste.

Estimated food waste is based on a simple scaling function taking the UK average as “frequently”.

Sources

Updates and model specifications

  • Per Person model
  • UK data

Pet Footprint

Pet carbon, land and water footprints are calculated for a household based on the number of pets (average or actual) and the carbon, land and water usage related to their food.

Average pet numbers are taken from the Pet Food Manufacturer’s pet population survey adjusted for the number of people in the UK.

Food footprints are calculated based on the calorie requirements of cats and different breeds of dogs which comes from Ohio State University’s Veterinary Centre whilst dog breed sizes are from the American Kennel Club. Cat breeds are taken from Wikipedia.

Calorie requirements are then multiplied by the average CO2e per calorie taken from a typical UK diet.

Sources

Updates and model specifications

  • Per Household model
  • Global data

Purchases

Clothing footprint

Clothing carbon and water footprints are calculated for a person based on the number of items purchases (average, estimated or actuals) multiplied by the amount of carbon or water used to produce each item.

Average items purchased are taken from the European Clothing Action plan in kg per person per year as is water usage per tonne. Carbon conversion factors are from Defra. Estimated clothing is based on group average weights (small, medium, large and footwear) with individual clothing weights estimated using information from delivery service companies. Final CO2e per item calculations are cross checked against individual LCA studies.

Sources

Updates and model specifications

  • Per Person model
  • UK model that can be used globally with average adjustments only

Appliances footprint

Appliance carbon footprints are calculated for the household based on consumption of appliances (average, actual) multiplied by the carbon emissions per unit. Consumption is estimated using ONS household spending surveys (Household appliances and Tools and equipment for house and garden) which gives total annual spending and adjusting to units purchased using a representative sample of appliance prices based on internet searches. Appliance calculations are split between small and large items.

Emissions per unit are taken from WRAP’s report “Reducing the Environmental Cost Impacts of Electrical Products” taking total embodied GHG and volume data to estimate per unit emissions.

Sources

Updates and model specifications

  • Per Household model
  • UK model (spending data)
  • Potential future further research: increase sample size of individual LCAs

Electricals footprint

Electrical item carbon footprints are calculated for a person based on the number of items purchased (average, actual) multiplied by the carbon footprint of each item. Average electrical items consumed are estimated using ONS spending data (Telephone equipment and Information processing equipment) and a reference value per electrical item. The wide range of electrical item price points makes this an approximation only.

Carbon footprints from electrical items are taken from individual LCAs (predominantly from Apple adjusted for production values only) and WRAP’s report “Reducing the Environmental Cost Impacts of Electrical Products” taking total embodied GHG and volume data to estimate per unit emissions.

Sources

Updates and model specifications

  • Per Person model
  • Global data for carbon footprints
  • UK data for spending
  • Potential future further research: increase sample size of individual LCAs

Personal care footprint

Personal care footprints are calculated for a person based on the amount spent on personal care items (average, estimated) multiplied by the CO2e per £ spent which, in turn, is based on LCA studies from personal care companies.

The average amount spent on personal care comes from ONS household survey data adjusted for average household size. Estimated amounts are simple ranges around the ONS average. CO2e per £ spent is calculated from company LCA studies which calculate per kilogram or item and adjusted for average item prices. As such the personal care footprints represent, at best, an approximation until a greater number of LCAs becomes available.

Sources

Updates and model specifications

  • Per Person model
  • UK data for averages. Global data for LCA

Household Cleaning footprint

Household cleaning footprints are calculated for a household based on the amount spent on household cleaning items (average, estimated) multiplied by the CO2e per £ spent which, in turn, is based on LCA studies.

The average amount spent on household cleaning comes from ONS household survey data (Cleaning materials) adjusted for average household size. Estimated amounts are simple ranges around the ONS average. CO2e per £ spent is calculated from LCA studies which calculate per kilogram or item and adjusted for average item prices. As such the household cleaning footprints represent, at best, an approximation until a greater number of LCAs becomes available.

Sources

Updates and model specifications

  • Per Person model
  • UK data for averages. Global data for LCA

Furniture footprint

Furniture footprints are calculated for a household based on the amount spent on furniture (average, actual) multiplied by the CO2e per item which, in turn, is based on LCA studies and Giki approximations.

The average amount spent on furniture comes from the ONS household survey data (Furniture and Furnishings) which is divided by the average price of a representative sample of products from internet research. CO2e per item comes from industry LCA studies and Giki approximations where no LCA has been found. The latter are based on furniture weight and material mix converted to CO2e using Defra conversion factors for different materials (wood, plastic, glass and soft furnishings).

Sources

Updates and model specifications

  • Per Household model
  • UK data for spending, global model for CO2e per unit
  • Further research: LCA studies to replace Giki estimates

Services

Recreational service footprint

Recreational footprints are calculated from UK carbon footprint data using approximations based on co2e to £ conversion provided by Defra.

UK carbon footprint data comes from Defra UK carbon footprint on a consumption basis. Segments included in line with ONS classifications.

Sources

Updates and model specifications

  • Per Person model
  • UK data

Mobile and internet footprint

Mobile and streaming footprints are calculated from UK carbon footprint data using approximations based on co2e to £ conversion provided by Defra. Internet usage is taken from Google sustainability report.

UK carbon footprint data comes from Defra UK carbon footprint on a consumption basis. Segments included in line with ONS classifications.

Sources

Updates and model specifications

  • Per Person model
  • Global data

Pharmacy footprint

Pharmacy product footprints are calculated from UK carbon footprint data using approximations based on co2e to £ conversion provided by Defra.

UK carbon footprint data comes from Defra UK carbon footprint on a consumption basis. Segments included in line with ONS classifications.

Sources

Updates and model specifications

  • Per Person model
  • UK data
  • Update Janaury 2021 - switch to co2e per £ for conversion factors to improve estimation process

Accommodation footprint

Accommodation footprints are calculated for a person based on accommodation night stays (average, estimated) multiplied by per night CO2e per occupied room.

Average accommodation night stays are taken from Statista using average overseas nights away for UK citizens. CO2e per night per room is from the CHSB Hotel footprinting tool looking at different hotel types for popular UK destinations (5stars, 4stars and 3stars in the UK, Spain, France and the United States). These are cross checked with Defra conversion factors for hotel stays.

Sources

Updates and model specifications

  • Per Person model
  • Global CO2e data, UK consumption data

Financial services footprint

Financial services footprints are calculated for a person based on the amount in £ (average, estimated, actual) of financial assets multiplied by the CO2e per £ of those assets.

Financial assets are separated into savings (bank accounts), investments (fixed rate bonds, bonds and equity investments including ISAs) and private pensions.

CO2e per £ invested are estimated by analysing the amount of carbon dioxide emitted, for both equity and debt financing, by fossil fuel companies from each of those financial asset groups. These estimates are calculated using CDP Scope 1&2 data for large fossil fuel companies (including Shell, Total, BP, Equinor, Occidental) and dividing by the total Enterprise Value (EV) to give a Scope1&2 CO2e per £ of EV. An equally weighted average of the different fossil fuel companies is taken with outliers removed. This is applied to investments and pensions.

CO2e per £ saved are estimated by analysing the lending by banks to fossil fuel companies, as a percentage of their overall loan book, using the same scaling factor from CDP data of carbon per unit of EV. This applies to savings.

More specifically for the three asset groups the methodology is as follows:

Savings. Three step process to estimate carbon emissions from financing. 1) Analysis of UK bank balances sheets to ascertain percentage of loan book that goes to fossil fuel industries 2) Calculate the amount of carbon emitted per £ of finance based on CDP data 3) combined the exposure to fossil fuel lending with the carbon emissions per unit of exposure to give an estimate of CO2e per £.

Investments. Three step process to estimate carbon emissions from Investments. 1) Analyse stock and bond market exposure to energy companies of a representative sample of balanced funds to ascertain percentage of investments that goes to fossil fuel industries. Assume a 50/50 split of investments between fixed rate bonds and stock and bond market investments. 2) Calculate the amount of carbon emitted per £ of finance based on CDP data 3) combined the exposure to fossil fuel investments with the carbon emissions per unit of exposure to give an estimate of CO2e per £.

Pension. Three step process to estimate carbon emissions from Investments. 1) Analyse stock and bond market exposure to energy companies of a representative sample of balanced funds to ascertain percentage of investments that goes to fossil fuel industries.2) Calculate the amount of carbon emitted per £ of finance based on CDP data 3) combined the exposure to fossil fuel lending with the carbon emissions per unit of exposure to give an estimate of CO2e per £.

Unlike other carbon footprints these measures represent carbon that is emitted on behalf of, rather than directly controlled by, individuals.

Sources

Updates and model specifications

  • Per Person model
  • UK consumption data, Global CO2e data

Trees

Tree planting footprint

Tree carbon footprints are calculated for a person based on the number of trees planted (average, estimated) multiplied by the amount of carbon each tree sequesters over a given time period.

The UK average is zero trees so any non-zero footprint result comes from a person entering trees they have planted in a given year. Tree carbon sequestration is calculated cumulatively using US Department of Energy Information looking at the average of slow, medium and fast growing conifers and hardwoods adjusting for survival rates over a period of time and multiplying carbon sequestered by the carbon / carbon dioxide equivalence ratio. The time period runs from the current date until 2025 and all numbers are negative.

Sources

Updates and model specifications

  • Personal data
  • Global model

Forest conservation footprint

Forest conservation footprints are calculated for a person based on the numbers of acres of rainforest protected (average, actual) multiplied by the amount of carbon saved by avoiding deforestation.

The UK average is zero so any non-zero footprint results comes from a person entering the acres they have protected in a given year. Carbon emissions avoided are calculated using a range of sources looking at different types of rainforest taking the mid point of estimates. Estimates are for a single time period only, i.e. more forests must be protected each time period in order to maintain the estimate.

Sources

Updates and model specifications

  • Per Person model
  • Global CO2e and UK consumption data

Giki Score

The Giki score provides a single measure to track your progress towards a sustainable life. It is calculated as an inverse function of an individual’s overall carbon footprint with additional points for committed steps, completed steps and footprints completed. A individual's carbon footprint is the most heavily weighted component of the score such that a high score, and in particular a score above 1000 which indicates that an individual has a carbon footprint that is aligned with a 1.5C lifestyle, can only be achieved with a low absolute carbon footprint.

Environmental impact savings

Carbon, water, land and single use plastic commitments and savings

The achievements section, which is included within Giki Zero Pro and the Household section, includes estimates of the carbon, land, water and single use plastic that may be saved either through committed, or completed action. Calculations for all savings are based on global averages, for high income countries, rather than the specific inputs of an individual user model or region. For example the savings for renewable electricity are calculated based on average electricity consumption with typical global grid conversion factors and the savings for reducing flying are based on average numbers of flights taken. For some people this will lead to an underestimation of potential savings (for example for a frequent flier) and for others an overestimation (for example someone who lives in a household with higher than global average electricity usage). To see the actual impact of steps taken an individual should therefore ensure that information in the Footprints page is updated when actions have been completed. Single use plastic is not calculated elsewhere in Giki Zero and is based on global averages, for high income countries.

Refinements

An individual can use average, estimated or actual data in Giki Zero’s Footprint models. In some cases estimates are taken from initial proxies (e.g. house electricity usage can be calculated looking at house size and house type) and then further refined by looking at other adjustments which may affect usage. For example in the case of electricity this includes whether an individual is using a green electricity tariff, whether they turn lights off and whether they limit the use of a tumble drier. Each refinement is individually researched to give an estimate of the impact it will have. However, for individuals who want a more personalised estimate they should enter actual information which will provide a better estimation process since it will reflect the actual quantities consumed. Taking electricity as an example again the total kwh consumed in a year will naturally provide a more precise carbon footprint that the estimation process almost irrespective of the number of additional estimation factors that are included.